During normal operation of various types of internal combustion engines, the surfaces of certain of the components thereof defining the combustion cavities attain temperatures within the range of 1500.degree.-1800.degree. F. which approach adiabatic wall conditions. Such temperatures prohibit the use of conventional sealing methods and cause metals to become inherently weak. Where ceramics are utilized as thermal barriers, they are oftentimes brittle and when subjected to concentrated sealing pressures are prone to fracture and, thus, deleteriously affect their thermal insulative qualities.